At the core of xdg-app is a small helper binary that uses Linux features like namespaces to set up sandbox for the application. The main difference between this helper and a full-blown container system is that it runs entirely as the user. It does not require root privileges, and can never allow you to get access to things you would not otherwise have.

This is obviously very useful for desktop application sandboxing, but has all sort of other uses. For instance, you can sandbox your builds to avoid them being polluted from the host, or you can run a nonprivileged service with even less privileges.

The current helper was a bit too tied to xdg-app, so as part of Project Atomic we decided to create a separate project based on this code, but more generic and minimal. Thus Bubblewrap was born.

Bubblewrap is a wrapper tool, similar to sudo or chroot. You pass it an executable and its argument on the command line. However, the executable is run in a custom namespace, which starts out completely empty, with just a tmpfs mounted as the root, and nothing else. You can then use commandline arguments to build up the sandbox.

For example, a very simple use of bubblewrap to run a binary with access to everything, but readonly: